In general, servovalves convert relatively low power electrical control input signals into a relatively large mechanical power output. FIG. 1 illustrates a conventional nozzle-flapper servovalve 10, such as a nozzle-flapper servovalve. The nozzle-flapper servovalve 10, for example, includes a housing 12 having a motor 14, a control shaft 16, an armature 17, a first nozzle 18, and a second nozzle 20. The control shaft 16 includes a flapper 22 oriented between the first nozzle 18 and the second nozzle 20 such that the flapper 22 defines a first gap 24 with the first nozzle 18 and defines a second gap 26 with the second nozzle 20. The nozzle-flapper servovalve 10 also includes a sleeve 28, a spool 30 disposed within the sleeve 28, and a feedback spring 32 coupling the armature 17 of the motor 14 to the spool 30.
During operation, when the motor 14 receives an input signal, such as from a controller, the motor 14 causes the spool 30 to meter fluid flow between a pressurized fluid source 34 and a hydraulic or fluid motor 36 coupled to the servovalve 10. In response to receiving a control signal, the motor 14 positions the armature 17 such that the armature 17 rotates the control shaft 16 and the flapper 22 causing the flapper 22 to impinge either the first nozzle 18 or the second nozzle 20. By impinging either the first nozzle 18 or the second nozzle 20, the flapper 22 causes an increase in fluid pressure (i.e. from a pressurized fluid source 35 via fixed orifices 37) in either a first chamber 38 or a second chamber 40, respectively, as defined by the housing 12 and the sleeve 28 and oriented at opposing ends 42, 44 of the spool 30.
In response to the increase in pressure, the spool 30 translates within the sleeve 28 to an open position. In the open position, lands 46-1, 46-2 of the spool 30 position relative to openings 48-1, 48-2 defined by the sleeve 28 to meter an amount of fluid flowing between the fluid source 34 and the fluid motor 36 to control positioning or movement of a load coupled to the fluid motor 36. As the spool 30 moves in response to the input signal, the spool 30 generates an opposing torque on the feedback spring 32. The torque on the feedback spring 32 repositions the flapper 22 to a substantially centered position relative to the nozzles 18, 20 and creates a force balance across the spool 30, thereby bringing the spool 30 to an equilibrium position.
As shown in FIG. 1, when the spool 30 positions in a null or closed position within the sleeve 28, such as in response to receiving a zero current control signal from a controller, each set of lands 46-1, 46-2 cover associated openings or ports 48-1, 48-2 oriented between the fluid source 34 and the fluid motor 36. In the null position, each set of lands 46-1, 46-2 minimizes fluid flow between the fluid source 34 and the fluid motor 36 via the ports 48-1, 48-2 to maintain a pressure gain within the servovalve assembly 10.
The position of the flapper 22, relative to the nozzles 18, 20, affects the pressure output of the servovalve 10. For example, assume the spool 30 orients in the null position within the servovalve 10 such that the servovalve produces a predetermined pressure output. Additionally, assume the flapper 22 also orients in a null position between the first nozzle 18 and the second nozzle 20 such that the first gap 24 (e.g., defined as the space between the flapper 22 and the first nozzle 18) is equal to the second gap 26 (e.g., defined as the space between the flapper 22 and the second nozzle 20). With such positioning of the flapper 22, the flapper 22 maintains equilibrium pressure within the first chamber 38 and the second chamber 40 of the servovalve 10, thereby maintaining the null position of the spool 30 within the servovalve 10 and maintaining the pressure output of the servovalve 10.
During the manufacturing process, however, due to manufacturing imprecision and tolerance stack-up errors, the manufacturer typically cannot position the flapper 22 in exactly the null position relative to the first nozzle 18 and the second nozzle 20. As such, the inexact positioning of the flapper 22 relative to the first nozzle 18 and the second nozzle 20 adjusts the pressures within the chambers 38, 40 (e.g., such that the pressure in the first chamber 38 is not substantially equal to the pressure in the second chamber 40), thereby affecting the pressure output of the servovalve 10. Prior to shipping the completed servovalve 10, therefore, the manufacturer measures the pressure output of the servovalve 10 to detect the positioning of the flapper 22 relative to the nozzles 18, 20.
Conventionally, during the testing procedure, the manufacturer disassembles a portion of the servovalve 10 and, using a test station, measures the pressure output of the servovalve 10. The partial disassembly provides the manufacturer with access to the flapper 22 and nozzles 18, 20 to allow repositioning of the nozzles 18, 20, based upon the measured pressure output. In the case where the test station indicates that the servovalve 10 does not produce a pressure output in accordance with specifications of the servovalve 10, the manufacturer physically repositions the nozzles 18, 20 within the servovalve 10, relative to the flapper 22. With the servovalve 10 connected to the test station, the manufacturer, using specialized tools, iteratively repositions the nozzles 18, 20 relative to the flapper 22 until the first gap 24 substantially equals the second gap 26 and the servovalve produces a pressure output in accordance with specifications of the servovalve 10. Such repositioning of the nozzles 18, 20 overcomes manufacturing imprecision and stack-up errors and allows positioning of the flapper 22 in a null position relative to the nozzles 18, 20.